Photoinduced Enhancement of Chemical Shift Sensitivity to Local Vibrations

Area of Science:

• Chemical Physics
• Molecular Spectroscopy
• Ultrafast Dynamics

Background:

• Time-resolved X-ray photoelectron spectroscopy (tr-XPS) using free-electron lasers allows real-time monitoring of chemical environments.
• Core-electron binding energy shifts provide insights into electronic excitation and nuclear motion interplay.
• This interplay is crucial for understanding molecular dynamics but remains underexplored.

Purpose of the Study:

• To investigate the link between electronic excitation and nuclear motion in fluoropyridine (C5H4FN) using combined theoretical and experimental approaches.
• To monitor the evolving chemical environment at nitrogen (N) and fluorine (F) atomic sites during relaxation from the photoexcited S1 state to the ground state via a conical intersection.

Main Methods:

• Utilized time-resolved X-ray photoelectron spectroscopy (tr-XPS) with novel free-electron laser sources.
• Performed combined theoretical and experimental studies on fluoropyridine (C5H4FN).
• Monitored core-electron binding energy shifts at N and F atomic sites.

Main Results:

• The fluorine (F) site primarily responded to vibrational relaxation, showing minimal sensitivity to the electronic excited state.
• Excitation to the S1 state induced a measurable energy shift at the nitrogen (N) site.
• The N site's sensitivity to local vibrations increased significantly due to electronic excitation, linked to photoinduced charge redistribution.

Conclusions:

• Electronic excitation and vibrational relaxation have distinct effects on different atomic sites within a molecule.
• Photoinduced charge redistribution plays a key role in modulating site-specific responses to electronic and vibrational dynamics.
• This study provides a foundation for exploring ultrafast dynamics and conical intersection pathways in complex molecules and materials.